The present invention relates to a mobile communication technique, and in particular, to a device for enhancing load distribution performance in a communication network used in a mobile communication system.
Recent mobile communication systems are constructed in a hierarchic configuration.
Description will be given of a WiMAX system as an example of the mobile communication system having a hierarchic configuration.
FIG. 23 shows an outline of the WiMAX system. The WiMAX system includes Mobile Stations (MS) 400 to 402, Base Stations (BS) 300 and 310, an access service network-gateway (ASN-GW) 200 to control the base stations, a Connectivity Service Network (CSN) 500, and a CSN 501 of a Mobile Virtual Network Operator (MVNO). Each of the CSN 500 and 501 includes functions of the triple A (AAA for Authentication, Authorization, and Accounting) associated with accounting and authentication. In a system supporting the mobile IP, the CSN 501 includes a Home Agent (HM). When internet services are provided, the CSN 500 and 501 are coupled with an internet 510.
In the hierarchic configuration of the WiMAX system, the ASN-GW 200 supervises a plurality of base stations 300 and 310 and the CSN 500 supervises a plurality of ASN-GW 200. One of the reasons why the mobile communication system is constructed in the hierarchic structure is implementation of mobility for the mobile stations 400 to 402. Assume, for example, that the mobile station 400 moves from the base station 300 to the base station 310. The start-point mobile station 300 and the end-point mobile station 310 are under control of one ASN-GW, i.e., the ASN-GW 200. Hence, it is possible for the ASN-GW 200 to detect the movement of the mobile station 400 to thereby continuously carry out an associated service, namely, to conduct handover of the service. Further, since the base stations 300 and 310 are installed at locations apart from the ASN-GW 200 in many cases, there is employed a network 520 between the base stations and the ASN-GW 200. The network 520 is coupled with an internet 511 depending on a communication enterprise as the owner of the network 520.
FIG. 24 shows a connection sequence of WiMax stipulated by the WiMAX Forum as an organization for standardization.
The mobile station 402, the base station 310, the ASN-GW 200, and the CSN 500 communicate messages conforming to the standard with each other to establish a wireless path 822 between the mobile station 402 and the base station 310, a GRE capsulation path 823 between the base station 310 and the ASN-GW 200, and a mobile IP path 825 between the ASN-GW 200 and the CSN 500. When accessing the internet, the mobile station 402 sends user data in the form of wireless data 7111 to the base station 310. When the user data is received, the base station 310 transfers the user data in the form of GRE capsulation data 7112 to the ASN-GW 200. The ASN-GW 200 sends the user data in the form of mobile IP capsulation data 7113 to the CSN 500. The CSN 500 transfers to the internet 510 the user data in the format of the user data transmitted from the mobile station 402.
FIG. 25 shows a packet format of the GRE capsulation data. This is a GRE packet format of GRE capsulation data between the base station and the ASN-GW. The GRE packet includes an IP header 7050, a GRE header 7051, and user data 7052. The user data 7052 is an IP packet transmitted from the mobile station 402. The IP header 7050 includes an IP address of the base station 310 and an IP address of the ASN-GW 200. These addresses are used as communication addresses of the base station 310 and the ASN-GW 200 terminating a GRE tunnel. The GRE header 7051 includes a GRE key prescribed by RFC2784 and RFC1701 and is used to identify the mobile station 402.
In the mobile communication system hierarchically configured as above, the user data communicated by the mobile station 402 travels as the wireless data 7111 via a wireless interval to the base station 310 and then to the ASN-GW 200 via the network 520 between the base station 310 and the ASN-GW 200 and arrives at the CSN 500. The CSN 500 extracts user data 7114 from the mobile IP capsulation data 7113 to transfer the user data 7114 according to an associated routing procedure.